Among the most powerful initiators for carbocationic polymerization of monoolefins are the Lewis Acids such as, for example, boron trifluoride and trichloride, aluminum trichloride, triethyl aluminum, diethyl aluminum chloride, ethylaluminum dichloride, titanium tetrachloride, antimony pentafluoride, and the like. Such carbocationic polymerization catalysts have many advantages, including high yield, fast reaction rates, good molecular weight control, and utility with a wide variety of monomers. However, conventional carbocationic polymerization processes typically employ Lewis Acid catalysts in unsupported form. Hence, these catalysts, typically, cannot be recycled or reused in a cost effective manner. In addition, these catalysts typically are at least partially soluble in the reaction media employed in conventional carbocationic polymerization processes and generally give rise to interactions which lead to partial complexation, dissolution and possible catalyst consumption. Use of these catalysts also results in at least some polymer contamination, thereby requiring various cleanup operations.
In a typical carbocationic polymerization process, such as the carbocationic polymerization of isobutylene, a catalyst feedstream in a liquid or gaseous form and a monomer feedstream are fed simultaneously into a conventional reactor. In the reactor, the streams are intermingled and contacted under process conditions such that a desired fraction of the monomer feedstream is polymerized. Then, after an appropriate residence time in the reactor, a discharge stream is withdrawn from the reactor. The discharge stream contains polymer, unreacted monomer and catalyst. In order to recover the polymer, the catalyst and unreacted monomer must be separated from this stream. Typically, there is at least some residue of catalyst in the polymer which cannot be separated. After separation, the catalyst is typically quenched and neutralized. The quenching and neutralization steps tend to generate large quantities of waste which typically must be disposed of as hazardous waste.
The recycling or reuse of Lewis Acid catalysts used in polymer processes is difficult because of the chemical and physical characteristics of these catalysts. For example, most Lewis Acid catalysts are non-volatile and cannot be distilled off; and some Lewis Acid catalysts are gaseous, such as BF.sub.3. The gases can be recycled and reused, but with considerably difficulty, by utilizing gas-liquid separators and compressors.
Accordingly, it would be desirable to avoid using gaseous, liquid or soluble Lewis Acid catalysts of this type and to employ a solid, heterogeneous catalyst on which initiation could take place, and which is insoluble in the polymerization reaction medium such that it will not be consumed during the polymerization process and such that it can be recovered from the reaction system by filtration.
The problem in the search for suitable solid state Lewis Acid catalysts is linked with the fact that heterogeneous catalysts typically are less reactive than homogeneous catalysts, since such solid state, heterogeneous catalysts are active only at their surface, i.e., any active chemicals located inside the mass or body of such catalysts are prevented from initiating the desired polymerization reaction since they cannot physically contact the monomers being polymerized.
Even so, certain solid state catalysts have been studied for use in the carbocationic polymerization of olefins. For example, Sket et al (B. Sket et al, J. Makromol. Sci.-Chem., A19(5), 643 (1983)) studied supported catalyst systems comprising boron trifluoride complexed with the aromatic rings of crosslinked poly(styrene) and poly(vinylpyridine). Similarly, Neckers et al (D. C. Neckers et al, J. Am. Chem. Soc. 94(26), 9284 (1972)) studied complexes between aluminum trifluoride and cross linked poly (styrene)-divinylbenzene, and Chung et al (in copending application Ser. No. 723,130, filed Jun. 28, 1991) disclosed the use of Lewis Acid catalyst systems comprising a Lewis Acid, preferably based on metals from Group III A, IV B and V B of the Periodic Table of Elements, supported on a functionalized thermoplastic polymer such as polypropylene-co-1-hexenyl-6-ol.
The concept of performing cationic polymerizations of 1-olefins in the presence of supported Lewis acid catalysts has been studied by other workers as well. See, for example, Y. A. Sangalov et al, Dokl. Akad. Nauk. SSSR, 265(3), 671 (1982). In all these cases, it can be considered that the catalysts are at least partially soluble in the reaction medium, but that they are immobilized due to the fact that they are complexed to an aromatic nucleus or to a functional group borne on a polymer support. A disadvantage of immobilized Lewis Acid catalysts of this type is that the reaction complexation involved in the immobilization of the Lewis Acid on the polymer support is more or less reversible and that the Lewis acid can be released from the support and into the polymerization products, even if the release process is slow.
There have been several attempts made to support Lewis Acid catalysts on the surface of inorganic substrates such as silica gel, alumina, graphite and clay. Although these approaches are somewhat successful in recycling the Lewis Acid catalysts, there are several disadvantages associated with their use. One particularly strong disadvantage is that these approaches to supported catalysts generally produce only low molecular weight oligomers. Another disadvantage is that the catalysts (supported on inorganic substrates) typically leach out during the reaction since the catalysts tend to not be fixed firmly to the supporting substrates.
U.S. Pat. No. 3,255,167 discloses olefin polymerization in the presence of reduced titanium halide supported on gamma-alumina. The catalyst is prepared by impregnating gamma alumina with titanium tetrachloride and subjecting the impregnated composition to reducing conditions, for example, by passing hydrogen gas through the impregnated alumina under elevated temperature conditions.
U.S. Pat. No. 3,721,632 discloses a catalyst comprising a metal halide based on metals of Group I A, I B, II B, III B and VIII A on a support such as diatomaceous earth, charcoal, alumina, silica, or silica-alumina.
U.S. Pat. No. 4,112,011 discloses a catalyst comprising gallium compounds on a suitable support such as aluminas, silicas and silica-aluminas.
U.S. Pat. No. 4,116,880 discloses a catalyst comprising a fluorinated graphite support having certain Lewis Acids bonded thereto. The Lewis Acids are selected from the halides of the metals of Group II A, III A, IV B, V A, V B or VI B.
U.S. Pat. Nos. 4,288,649, 4,306,105, 4,582,818 and 4,542,301 disclose halided alumina catalysts which are useful for the various hydrocarbon conversion reactions, as well as for the polymerization of olefins. The catalysts typically are prepared by contacting an alumina support with a halogenating agent such as chlorine gas, thionyl chloride or phosgene at elevated temperatures.
U.S. Pat. No. 3,629,150 discloses catalysts suitable for polymerizing isobutene, wherein the catalysts are prepared by reacting dehydrated silica having silanol groups with aluminum alkyl, and then with a hydrogen halide or with an alkyl halide.
U.S. Pat. Nos. 3,925,495, and 3,984,352 and British Patent Application GB 2,001,662 A disclose catalysts consisting of graphite having a Lewis Acid intercalated in the lattice thereof.
U.S. Pat. No. 4,235,756 discloses a catalyst comprising porous gamma alumina impregnated with an aluminum hydride.
U.S. Pat. Nos. 4,719,190, 4,798,190 and 4,929,800 disclose hydrocarbon conversation and polymerization catalysts prepared by reacting a solid adsorbent containing surface hydroxyl groups with certain Lewis Acid catalysts in halogenated solvent. The only disclosed adsorbents are inorganic; namely, silica alumina, boron oxide, zeolite, magnesia and titania.
In all cases where a Lewis Acid is supported on an inorganic support, however, there is a risk either of leaching of the solid catalyst from the support or of loss of activity of the catalyst due to the reaction (or interaction) responsible for the fixation of the active species on the support.
It is known that some solids exhibit Lewis acidity so that it is possible to initiate carbocationic polymerization on their surface. For example, solid superacids such as SO.sup.2- /Fe.sub.2 O.sub.3 or SO.sub.4.sup.2- /TiO.sub.2 were reported to be active for the polymerization of alkyl vinyl ethers (M. Hino et al, Chem. Lett. (1980, 963). However, it seems that these catalysts owe their activity to the presence of sulfur atoms with covalent SO double bonds (K. Tanabe et al, Successful Design of Catalysts, p. 99, T. Inui Ed., Elsevier Sci. Publish. Amsterdam (1988)). Polymerization catalysts of this type tend to lose their activity, and more importantly they are active at too high a temperature to be used for the polymerization of olefin monomers such as isobutylene and 1-butene. Moreover, the fact that such superacid catalysts might effectively initiate vinyl ether polymerization does not necessarily imply that they might actively initiate the polymerization of other olefin monomers, such as 1-olefins, since the 1-olefins generally are less reactive that vinyl ethers.
U.S. Pat. No. 4,116,880, which has been discussed hereinabove, also discusses superacid catalysts which are supported, for example, on fluorinated alumina, on inert polyfluorinated polymer supports such as polytetrafluoroethylene (Teflon), or on fluorinated polycarbon (coke).
European Patent No. 273,627, discloses that granular aluminum trichloride was found to be active as a polymerization catalyst. It was also disclosed by Collomb et al, in Europ. Polym, J., 16(2), 1135 (1980), that certain transition metal perchlorates and trifluoromethanesulfonates were active for the cationic polymerization of isobutylene. However, the Collomb et al investigation of heterogenous catalyst systems was limited to salts of metals of the first tread of Group VIIIa, i.e. Fe, Ni and Co, and of Groups I A, I B, II A, II B, and III B. It was also noted by Collomb et al that water was detrimental to the polymerization initiating activity.
Marek et al (M. Marek et al, Makromol. Chem. Symp. 13/14, 443 (1988)) reported that the combination of ferric chloride with boron trichloride, titanium tetrachloride or vanadium oxychloride proved to be active for catalyzing the polymerization of olefins. However, Marek et al specified that the activity only concerns polymerization in solution initiated by the soluble fraction of the various initiator systems.
Lewis Acids useful as catalysts in carbocationic processes as well as carbocationically polymerizable monomers, and, the polymers produced from such processes are disclosed and described in the following publications: 1) Cationic Polymerization of Olefins: A Critical Inventory, Kennedy, Joseph P., John Wiley & Sons, New York (1975), and, 2) Carbocationic Polymerization, Kennedy, Joseph P., John Wiley & Sons, New York (1982).
In spite of the advances made in the field of polymerization catalysis, there has been a continuous search for catalysts having high efficiency which can be recycled or reused in cationic polymerization processes. The present invention was developed pursuant to this search.